1. Field of the Invention
The present invention relates to a gas separation apparatus for separating specific gases from a mixture gas containing a plurality of gases.
2. Description of the Related Art
Conventionally, various gases are used in semiconductor manufacturing processes depending on the process. For example, perfluoro compound (PFC) gas which is a mixture containing fluorine compounds such as CF4, NF3, C2F6, C3F8, SF6, and CHF3 is used as a reaction gas at the dry etching process or at the thin film forming process. In these processes, discharge gas is produced which contains the PFC gas.
Because these discharge gases such as PFC cannot be discharged out of the manufacturing line as such, various methods are employed for treating these gases. The treating methods include (i) decomposition in which the PFC gas is decomposed by combustion, catalyst heating, or plasma decomposition; (ii) membrane separation in which these materials are separated by a membrane; and (iii) subzero cooling separation in which the separation is achieved taking advantage of the difference in the boiling points of the gases.
However, in the above method (i), there are shortcomings in that a complete decomposition is difficult and the gas cannot be recovered for reuse because the gas is decomposed and discharged. In the membrane separation (ii), although nitrogen in the discharge gas can be removed, the separation between CF4 and NF3 or the like which have similar molecular size is difficult. In the above method (iii), the overall size of the apparatus becomes large, resulting in increased cost for the equipment and increased running cost. Moreover, because the boiling point difference between CF4 and NF3 is only 1xc2x0 C., the separation is difficult.
One object of the present invention is to provide a gas separation apparatus capable of separating a mixture gas having a plurality of gas constituents inexpensively and with high purity.
In order to achieve the object mentioned above, according to one aspect of the present invention, there is provided a gas separation apparatus for separating specific gases from a mixture gas to be treated containing the specific gases, the apparatus comprising: a concentrator for concentrating the specific gases within the mixture gas to be treated; and a separator for chromatographically separating the mixture gas, with the specific gases concentrated by the concentrator, into each of the plurality of gas constituents.
In this manner, by using a separator which performs chromatographic separation, separation of specific gases, such, for example, as CF4 and NF3, contained in the mixture gas to be treated, which are otherwise difficult to be separated, can be reliably achieved. The separated CF4 and NF3 can then be recovered and reused.
By providing a concentrator before the separator, the specific gases, for example, CF4 and NF3 can be reliably separated at the separator.
According to another aspect of the present invention, there is provided a gas separation apparatus for separating specific gases from the mixture gas to be treated containing the specific gases, the apparatus comprising: a separator for chromatographically separating the mixture gas to be treated into each of the plurality of gas constituents; and concentration means for independently a concentrating the mixture gas separated into each of the plurality of gas constituents and obtained at the separator; wherein the concentrated gases obtained by the concentrator are recovered and reused.
A carrier gas (for example, nitrogen) is included in the chromatographically separated specific gases, such, for example, as CF4 and NF3. By removing the carrier gas by the concentration means, the specific gases can be recovered and reused.
According to another aspect of the present invention, there is provided a gas separation apparatus for separating specific gases from a mixture gas to be treated containing the specific gases, the apparatus comprising: a front concentrator for concentrating the specific gases within the mixture gas to be treated; a separator for chromatographically separating the gases, with the specific gases concentrated by the upstream concentrator, into each of the plurality of constituents; and rear concentrators for independently concentrating the mixture gas separated into each of the plurality of gas constituents and obtained at the separator; wherein the concentrated gas obtained by the rear concentrators are recovered and reused.
With this apparatus, the specific gases can be separated effectively and in high concentrations. Therefore, each of the obtained specific gases can be easily reused.
According to another aspect of the present invention, it is preferable that a mixture gas containing the specific gases having a plurality of gas constituents is the PFC gas discharged from a semiconductor manufacturing process and the mixture gas to be treated contains nitrogen as another gas.
According to another aspect of the present invention, it is preferable that the PFC gas contains one of fluorine compounds having at least one of the elements C, N, and S as a composition element.
According to another aspect of the present invention, it is preferable that the PFC gas includes one of CF4, NF3, C2F6, C3F8, SF6, or CHF3.
According to another aspect of the present invention, it is preferable that the above-mentioned concentration means is either a membrane separator which takes advantage of the permeability/impermeability of a membrane or a subzero cooling separator which takes advantage of the difference in boiling point. With such a concentration means, concentration of the PFC gas, for example, can be effectively performed.
According to another aspect of the present invention, it is preferable that a plurality of chromatographic columns are provided and used in sequence. By using a plurality of columns, the separation process can be performed almost continuously.
According to another aspect of the present invention, it is preferable that the gases other than the specific gases separated at the separator contains nitrogen as its main constituent and the nitrogen gas is reused in a given usage.
According to another aspect of the present invention, it is preferable to perform a process to remove gas constituents other than the nitrogen gas on the gas containing nitrogen gas as its main constituent.